Process And Plant For The Removal Of Metals By Biosorption From Mining Or Industrial Effluents

ABSTRACT

A method and a plant to remove metals by biosorption from mining or industrial effluents comprising: (a) subject the effluent to at least one first stage of pre-treatment, selecting among: precipitation by pH rising, solvent extraction or solvent extraction on emulsified membranes in order to reduce its load of metals to a concentration level that allows it to be treated by the next stage of biosorption, and (b) subject the liquid that has been previously in the stage of pre-treatment to a second stage of continuous metals removal by biosorption. To perform the continuous metals removal by biosorption is supplied a group of reactors, constituted for at least one, or at least two or at least three fixed bed bioreactors, which packing material has been colonized with a biofilm formed by a bacterial culture or a mixture of microorganisms with the capacity of binding metals by biosorption; pre-treated water is led to the group of bioreactors, the treated effluent comes from this last one and is led to the discharge of the plant.

FIELD OF THE INVENTION

This invention relates to a process and a bioremediation plant, employedto biologically remove heavy metals by attached microorganisms.

BACKGROUND OF THE INVENTION

Traditionally, physical-chemical methods have been used to remove metalsfrom industrial and mining effluents, being the precipitation by risingthe pH of the solution the simplest method to perform this operation.However, the permitted levels for metals discharge to surface andunderground water bodies are, in some cases, lower to those that can beachieved by this system. For this reason, other additional alternativesfor the metals removal have been studied.

In an interesting recent review, Blais et al. (2000). State of the artof technologies for metal removal from industrial effluents. Rev. Sci.Eau 12 (4): 687-711, described in detail the state of development ofeach of them. Among the metals removal and recovering processes are:precipitation, absorption and biosorption, electro-winning andelectrocoagulation, cementation, membrane separation (reverse osmosisand electrodialysis), solvent extraction and ion exchange.

In Table 1 are shown the performance characteristics of thesetechnologies. This information clearly proves that efficiency depends onthe tolerance degree of the technologies to the conditions of theeffluent and on the required levels of treatment. In this sense, as wewill see later, biosorption is a technology that makes possible theremoval of metals in order to reach low levels of pollution. Thus, thechoice of a suitable pollution control technology depends on severalfactors, such as:

-   -   discharge fate    -   metal type and its concentration    -   other contaminants in the water    -   decontamination level required    -   treatment costs

TABLE 1 Performance characteristics of some metal removal and recoverytechnologies (modified from Eccles (1998) Treatment ofmetal-contaminated wastes: why select a biological process? TrendsBiotechnol. 17, pp. 462-465.) Appropriated Work Suspended Tolerance toLevel for Metals Solids Organic Metal Technology pH Change SelectivityInfluence Molecules (mg/L) Hydroxide Tolerant Non- Tolerant Tolerant >10Precipitation Selective Sulfide Limited Limited Tolerant Tolerant >10Precipitation Tolerance Selectivity (according to pH) Adsorption LimitedModerated Gets fouled Can suffer <10 tolerance poisoning ElectrochemicalTolerant Moderated Can be handled Can be adjusted >10 to become tolerantMicrofiltration Limited Moderated Gets fouled Non-Tolerant >10 Ionexchange Limited The Gets fouled Can get <100 Tolerance coordinatingpoisonous resins can be selective Solvent Tolerance in There are Getsfouled Non-Tolerant >100 extraction some selective systems extractantsfor metals Biosorption** Limited Moderated Gets fouled Tolerant <10Tolerance **added to comparison

As the environmental restrictions have become more rigorous and thedischarge limits of emission have dropped, more environmentally friendlymetal production processes are required.

STATE OF THE ART

Biosorption is understood as the uptaking of heavy metals by a part ofthe biomass (living or nonliving) only by physical-chemical mechanisms.In general terms, the biosorption process has been described as anon-selective mechanism that allows the removal of the following metals:Ag, Al, Au, Co, Cd, Cu, Cr, Fe, Hg, Mn, Ni, Pb, Pd, Pt, U, Th, Zn, andothers (Gadd y White (1993). Microbial Treatment of Metal Pollution—AWorking Biotechnology? Trends Biotechnol., 11, 353-359).

Nowadays, there is a large amount of international scientific literatureabout the capability of some microorganisms of concentrating metal ionsby biosorption from dilute solutions, among them we can mention Castroet al. (1992), Biomasa de Rhizopus oligosporus como adsorbente de ionesmetálicos. Microbiología SEM 8, 94-105, Cotoras et al. (1992)Biosorption of metal ions by Azotobacter vinelandii. World Journal ofApplied Microbiology and Biotechnology 8, 319-323, Cotoras et al. (1992)Sorption of metal ions by whole cells of Bacillus and MicrococcusEnvironmental Technology 13, 551-559, Fourest y Roux (1992), Heavy metalbiosorption by fungal mycelial by-products: mechanism and influence ofpH. Appl. Microbiol. Biotechnol. 37 pp. 399-403, Holan y Volesky (1995),Accumulation of cadmium, lead and nickel by fungal and wood biosorbents.Appl. Biochem. Biotechnol. 53 pp. 133-142. The research works havecovered different groups of organisms, among which are: bacteria (e.g.E. coli, Zoogloea ramigera, Bacillus subtilis, Azotobacter vinelandii,etc.), fungi (e.g. Rhizopus arrhizus, Aspergillus niger) and alga (e.g.Chlorella vulgaris, Sargassum sp.). From all of these researches it ispossible to conclude that microorganisms can concentrate importantamounts of metal ions. Values of biosorption from 0.3% to 35% of themicrobial dry weight when using solutions with metals concentrationbetween 10 and 100 mg/L have been published. In some cases, metalremoval from the solution overcomes the 99% of efficacy (Gadd y White(1993). Microbial Treatment of Metal Pollution—A Working Biotechnology?Trends Biotechnol., 11, 353-359).

Researches about the Application of Biosorption in the Removal of Metalsfrom Industrial Effluents.

Besides the purely scientific studies about this matter, biosorption hasalso been studied as an economical system for metal removal fromindustrial effluents by means of living biomass, nonliving biomass orits derivatives. There are numerous reviews about the state ofdevelopment of the biosorption application and its advances. Among themare: Kratochvil D. y B. Volesky, Advances in the biosorption of heavymetals, Trends Biotechnol. 16 (1998), pp. 291-300; Volesky B. y Z. R.Holan, Biosorption of heavy metals, Biotechnol. Prog. 11 (1995), pp.235-250; Kapoor, A. y Viraraghavan, T. (1995), Fungal Biosorption—AnAlternative Treatment Option for Heavy Metal Bearing Wastewaters: AReview. Bioresource Technology, 53, 195-206; y White, C et al. (1995),The Role of Microorganisms in Biosorption of Toxic Metals andRadionuclides. International Biodeterioration & Biodegradation, 17-40.This background information have been summarized in the review articleby Volesky, Detoxification of metal-bearing effluents: biosorption forthe next century Hydrometallurgy Volume 59, 203-216 (2001).

One of the most relevant requirements for the technological applicationof biosorption is the biomass fixation to an attaching medium in orderto allow the biosorbent to be kept in a reactor, so it can be reused.This have been performed frequently by immobilizing the microorganismson a matrix.

There are many examples of the application of these methodologies, themost representative can be found in the following scientific researches:Brierley, Production and application of a Bacillus-based product for usein metals biosorption. In: B. Volesky, Editor, Biosorption of HeavyMetals, CRC Press, Boca Raton, Fla. (1990), pp. 305-312; Brierley yBrierley, Immobilization of biomass for industrial application ofbiosorption. In: A. E. Torma, M. L. Apel and C. L. Brierley, Editors,Biohydrometallurgical Technologies, Proceedings of the InternationalBiohydrometallurgy Symposium, The Minerals, Metals and MaterialsSociety, Warrendale, Pa. (1993), pp. 35-44; Tsezos y Deutschmann (1990).An Investigation of Engineering Parameters for the use of ImmobilizedBiomass Particles in Biosorption. J. Chem. Technol. Biotechnol., 48,29-39; Gilson y Thomas (1995), Calcium alginate bead manufacture: withand without immobilised yeast. Drop formation at a two-fluid nozzle. J.Chem. Technol. Biotechnol. 62 pp. 227-232; Bedell y Damall, (1990),Immobilization of nonviable, biosorbent, algal biomass for the recoveryof metal ions. In: B. Volesky, Editor, Biosorption of Heavy Metals, CRCPress, Boca Raton, Fla., pp. 313-326; Figueira et al. (2000),Biosorption of metals in brown seaweed biomass. Water Res. 34 pp.196-204; Kratochvil et al. (1997) Optimizing Cu removal/recovery in abiosorption column. Water Res. 31 pp. 2327-2339; Kratochvil y Volesky,(2000), Multicomponent biosorption in fixed beds. Water Res. 34 pp.3186-3196; Trujillo et al, (1991), Mathematically modeling the removalof heavy metals from wastewater using immobilized biomass. Environ. Sci.Technol. 25 pp. 1559-1565.

Among all these studies on immobilization are the remarkable works bythe Brierley couple (Brierley, Production and application of aBacillus-based product for use in metals biosorption. In: B. Volesky,Editor, Biosorption of Heavy Metals, CRC Press, Boca Raton, Fla. (1990),pp. 305-312; Brierley y Brierley, Immobilization of biomass forindustrial application of biosorption. In: A. E. Torma, M. L. Apel andC. L. Brierley, Editors, Biohydrometallurgical Technologies, Proceedingsof the International Biohydrometallurgy Symposium, The Minerals, Metalsand Materials Society, Warrendale, Pa. (1993), pp. 35-44), who createdan immobilized biosorbent product based on a bacterium (Bacillussubtilis). The microalgae immobilization of the Darnall's research group(Bedell y Darnall, (1990), Immobilization of nonviable, biosorbent,algal biomass for the recovery of metal ions. In: B. Volesky, Editor,Biosorption of Heavy Metals, CRC Press, Boca Raton, Fla., pp. 313-326),the immobilized brown seaweed of the Volesky's group (Figueira et al.(2000), Biosorption of metals in brown seaweed biomass. Water Res. 34pp. 196-204; Kratochvil et al. (1997) Optimizing Cu removal/recovery ina biosorption column. Water Res. 31 pp. 2327-2339; Kratochvil y Volesky,(2000)) and the Jeffers's pellet-shaped product named BIO-FIX (Trujilloet al, (1991), Mathematically modeling the removal of heavy metals fromwastewater using immobilized biomass. Environ. Sci. Technol. 25 pp.1559-1565.) The immobilizing agents or the most commonly used matrixesare alginate, polyacrylamine, polysulfone, silica, cellulose andglutaraldehyde.

The development of biosorbent materials has also led to the obtainmentof a large amount of patents related to this subject. Thus, Volesky, etal., (1988) patented a method for gold biosorption using the biomass ofa brown seaweed attached by a natural or synthetic polymer (U.S. Pat.No. 4,769,223). In the 90's decade, the greatest part of the patentsfollowed this example, promoting the production of pellets-shapedbiosorbents by the artificial uptaking or immobilization of the biomass.This focus is also applied by the following patents: Brierley, et al.(1990, U.S. Pat. No. 4,898,827) they use immobilized Bacillus subtiliswith the metal binding capacity of this bacterium, Greene, et al. (1991,U.S. Pat. No. 5,055,402) they used immobilized microalgae at high levelsof temperature (300° C. to 500° C.). It is also important to state thedevelopment of polymer beads, such as polysulfone to immobilize sorbents(Jeffers, et al., 1994, U.S. Pat. No. 5,279,745) which constitutes thebase for BIO-FIX, developed by the Bureau of Mines of the United States.More recently, the following processes of preparation of biosorbentshave been published: crosslinked yeasts by aldehydes (Yannai, et al.1996, U.S. Pat. No. 5,538,645) biological material beads immobilized byneutralized and crosslinked poli-(acid carboxylics) adhesives (Summers,Jr., et al. 1997, U.S. Pat. No. 5,602,071), brown seaweed which alginatehas been extracted (Pohl 1997, U.S. Pat. No. 5,648,313), fungicalbiomass (of the types of Aspergillus, Penicillium and Trichoderma) ofbacterial (Micrococcus) treated with phosphoric acid, solvents andsodium hydroxide (Kogtev, et al. 1998 U.S. Pat. No. 5,789,204),microorganisms immobilized in hydrophilic polyurethane (Hermann 1999,U.S. Pat. No. 5,976,847).

Although these biosorbent materials are promising, they show thefollowing disadvantages:

-   -   They need a biomass concentration stage (e.g. centrifugation)        mixed with the immobilizing agent and subsequent reaction of        gelling.    -   They use chemical agents potentially hazardous and/or expensive        (e.g. dimethylformamide (DMF) used during the production process        of BIO-FIX).

On the other hand, Diels, et al. (2000, U.S. Pat. No. 6,013,511)described metals bioprecipitation by using biofilms formed in a side ofvery singular membranes, made of an inorganic oxide and an organicpolymer. Nevertheless, this process requires the constant addition ofnutrients on the other side of the membrane to keep the microorganismsalive.

Cotoras and Viedma (2000, Chilean Patent Register 40704) published aprocess in which, first of all, a biofilm is formed spontaneously on aninert support and low-priced material. Once the immobilization isfinished, the alternated cycles of biosorption and desorption start.Particularly, this is about a process to remove or recover metal ions bybiosorption from industrial or mining effluents that includes thefollowing stages: a) growing and immobilization of the biomass in thebioreactor, b) transfer the solution with metal ions, and c) elute themetal ions uptaken by the bacterial biomass. This process presents thefollowing advantages that make it more attractive for an industrialapplication:

-   -   It does not require complex stages of production because the        natural attachment capacity of the bacteria is employed.    -   It does not require the use of chemical agents, which are        potentially hazardous and/or too expensive.    -   It uses different raw materials and supplies available at a        local scale, depending on the area in which the technology is        applied.

In spite of the many advantages of the biosorption process in comparisonto the alternative physical-chemical methods, there are some obstaclesthat make it difficult to apply this process for the removal of metalions from industrial or mining effluents. One of these difficulties isthe fast metal-saturation produced when treating liquid or industrialresidues containing relatively high concentrations of metals (e.g., 50to 100 mg/L of copper). On the other hand, it arises the problem thatwhen saturation of the biomass is produced, the process must beinterrupted and a desorption operation along with a subsequent wash mustbe performed, in order to regenerate the metal removal capacity of thebiosorbent material. This is an important disadvantage that restrains acontinuous type of treatment like the industry and mining need todecontaminate their effluents.

This invention presents a series of alternatives to the disadvantages ofthe technologies available in the state of the technique, by the designof a process and a plant that allows the operation of the system in adiverse range of metals concentration to be treated, included effluentswith high metals concentration and the continuous functioning of boththe process and the plant. This is achieved by a pre-treatment stagethat adjusts the levels of metal concentration and/or pH to therequirements of the biosorption stage. The result of the combination ofthese stages has the singularity of being synergical, because it notonly overcomes the problem of the fast saturation of the microbialbiomass due to the high metals concentration, but also it surpasses theobstacle of the physical-chemical systems of metals removal. Thepre-treatment system is also employed to eliminate the concentratedmetals generated during the desorption of the biosorption stage. Thecontinuous operation of the whole process and the plant, in itspreferred embodiment, is reached by using a group of bioreactors ofbiosorption that are alternated, according to its level ofmetal-saturation.

SUMMARY OF THE INVENTION

The main object of this invention is a method for the removal of metalsby biosorption from mining or industrial effluents which comprises:

(a) subjecting the effluent to, at least, one first stage ofpre-treatment, selecting among: precipitation by pH rising, solventextraction or solvent extraction on emulsified liquid membranes, toreduce its load of metals to concentrations that can be treated in thenext stage of biosorption; and(b) subjecting the liquid that has been previously treated at thepre-treatment stage to a second stage of continuous removal of metals bybiosorption, in which microbial biomass is grown and immobilized in abioreactor, towards which the water to be treated is led and, finally,the metal ions uptaken by the biomass are eluted.

In a preferred embodiment of this invention the stage of metalscontinuous removal by biosorption comprises:

(b1) providing of at least one fixed bed bioreactor, which packingmaterial can be colonized with a biofilm, formed by a microbial cultureor a mixture of microorganisms with the metal binding by biosorptioncapacity;(b2) always perform the colonization of the packing material of said atleast one bioreactor by using microorganisms when starting thefunctioning of the treatment method; said colonization is carried out byadding culture medium to the bioreactor, inoculating it with theattaching microorganism and subjecting the culture to aeration,agitation and temperature control for the suitable period of time toobtain the effective colonization of the support material of said atleast one bioreactor, once the culture is finished, the culture mediumis taken away and said at least one bioreactor is ready to be used inthe biosorption stage;(b3) leading the pre-treated water to said at least one bioreactor fromwhich the treated effluent is obtained and led to the discharge of theplant;(b4) when the biosorption capacity of said at least one bioreactor getssaturated, subjecting said at least one bioreactor to a desorption andneutralization treatment to regenerate the biosorption capacity of thebiofilm attached to the support material of said at least onebioreactor, said desorption is performed by adding a solution with adesorbent agent, as an acid solution, with the capability of displacethe metals bound to the microorganisms, obtaining an acid solutionloaded with metal ions, which is reused in a new desorption process oris led to the beginning of the process, mixing it with the effluententering to the pre-treatment;(b5) performing, finally, the neutralization of said at least onebioreactor, adding a base solution to set the pH value close to theneutral point, in order to improve the biosorption capacity; and(b6) performing the recolonization of the fixed bed using microorganismsto replace the microbial film when, after many cycles of biosorption,desorption and neutralization, the metal removal capacity begins todiminish, said colonization is performed by adding culture medium tosaid at least one bioreactor, inoculating it with the attachingmicroorganism and subjecting the culture to aeration, agitation andtemperature control for a suitable period of time to obtain theeffective colonization of the support material of said at least onebioreactor, once the culture is finished the culture medium is takenaway and said at least one bioreactor is ready for being employed againin the biosorption stage.

In a second preferred embodiment of this invention, the continuousmetals removal by biosorption stage comprises:

(b1) providing of at least two fixed bed bioreactors, which packingmaterial can be colonized with a biofilm formed by a microbial cultureor a mixture of microorganisms with the metal binding by biosorptioncapability;(b2) always perform the colonization of the packing material of said atleast two bioreactors using microorganisms when starting the functioningof the treatment method, said colonization is performed by addingculture medium to said at least two bioreactors, inoculating them withthe attaching microorganism and subjecting the culture to aeration,agitation and temperature control for a suitable period of time toobtain the effective colonization of the support material of said atleast two bioreactors, once the culture is finished, the culture mediumis taken away and said at least two bioreactors are ready to be employedin the biosorption stage;(b3) leading the pre-treated water to a first bioreactor of one of saidat least two bioreactors from which one the treated effluent is obtainedand led to the discharge of the plant; meanwhile, a second bioreactorfrom one of said at least two bioreactors that presents full biosorptioncapacity is kept;(b4) when the biosorption capacity of said first bioreactor getssaturated, leading the pre-treated water to said second bioreactor thatwas kept, now from this last one the treated effluent is obtained andlead to the discharge of the plant;(b5) subjecting said first bioreactor, meanwhile and simultaneously, toa treatment of desorption and neutralization, to regenerate thebiosorption capacity of the biofilm attached to the support material ofsaid first bioreactor, said desorption is performed by adding a solutionwith a desorbent agent, just like an acid solution, that can displacethe metals bound to the microorganisms, obtaining an acid solutionloaded with metal ions, which is reused in a new process of desorptionor is lead to the beginning of the process, mixing it with the effluententering to the pre-treatment;(b6) performing, finally, the neutralization of said first bioreactor,adding a base solution that allows to set the pH value close to theneutral point, in order to improve the biosorption capacity; and(b7) repeating from the previous stage b4, performing a rotation of saidat least two bioreactors when that one of said at least two bioreactorsthat receives the pre-treated effluent gets saturated again, and whereinsaid that one of said at least two bioreactors can be said firstbioreactor or said second bioreactor; and(b8) performing the recolonization of the fixed bed using microorganismsto replace the microbial film when, after many biosorption, desorptionand neutralization cycles, its metal removing capacity begins todiminish, in this case, the recolonization of the fixed bed is performedin said first or second bioreactor that has finished the biosorption andneutralization phase, where said colonization is produced by addingculture medium to said first or second bioreactor, inoculating it withthe attaching microorganism and subjecting the culture to aeration,agitation and temperature control for a suitable period of time toobtain an effective colonization of the support material of said firstor second bioreactor, once the culture is finished, the culture mediumis taken away and said first or second bioreactor is ready to be usedagain in the biosorption stage.

In a third preferred embodiment of this invention, the continuous metalremoving by biosorption stage comprehends:

(b1) providing of at least three fixed bed bioreactors, which packingmaterial can be colonized with a biofilm formed by a microbial cultureor a mixture of microorganism with the capability of binding metals bybiosorption;(b2) always performing the colonization of the packing material of saidat least three bioreactors using microorganisms when starting thefunctioning of the treatment method, said colonization is produced byadding culture medium to said at least three bioreactors, inoculatingthem with the attaching microorganism and subjecting the culture toaeration, agitation and temperature control for a suitable period oftime to obtain the effective colonization of the support material ofsaid at least three bioreactors, once the culture is finished, theculture medium is taken away and said at least three bioreactors areready to be used in the biosorption stage;(b3) leading the pre-treated water to a first bioreactor of said atleast three bioreactors and from this one to a second bioreactor of saidat least three bioreactors, connected in series, from this last one thetreated effluent is obtained, and led to the discharge of the plant;meanwhile, a third bioreactor of said at least three bioreactors, thatpresents a full biosorption capacity is kept;(b4) leading the pre-treated water to said second bioreactor when thebiosorption capacity of said first bioreactor gets saturated and fromthis one to said third bioreactor, connected in series, that was kept,now from this last one is obtained the treated effluent that is led tothe discharge of the plant;(b5) subjecting said first bioreactor, meanwhile and simultaneously, toa desorption and neutralization treatment, in order to regenerate thebiosorption capacity of the biofilm that is attached to the supportmaterial of said first bioreactor, said desorption is performed byadding a solution with a desorbent agent, just like an acid solution,that can displace the metals bound to the microorganisms, obtaining anacid solution loaded with metal ions, and which is reused in a newdesorption process or is led to the beginning of the process, mixing itwith the effluent entering to the pre-treatment;(b6) performing, finally, the neutralization of said first bioreactor,adding a base solution to set the pH value close to the neutral point inorder to improve its biosorption capacity;(b7) repeating from previous stage b4 performing a rotation of thebioreactors when that one reactor, from said at least three bioreactorsthat receives the pre-treated effluent, gets saturated again, whereinthat one bioreactor of said at least three bioreactors can be saidfirst, second or third bioreactor; and(b8) performing the recolonization of the fixed bed by microorganisms toreplace the microbial film when, after many biosorption, desorption andneutralization cycles, its metal removing capacity begins to diminish;in this case, the recolonization of the fixed bed is performed in thesame bioreactor that has finished the biosorption and neutralizationstage; said colonization is performed by adding culture medium to saidbioreactor; the said colonization is performed by adding culture mediumto said bioreactor, inoculating it with the attaching microorganism andsubjecting the culture to aeration, agitation and temperature controlfor a suitable period of time to obtain an effective colonization of thesupport material of said bioreactor, once the culture is finished theculture medium is taken away and said bioreactor is ready to be usedagain in the biosorption stage.

In a foreseen version of the invention, the microbial culture is abacterial or archaeal culture. In particular, the culture of bacteriacontains a population of selected bacteria among the genus Bacillus,Pseudomonas, Klebsiella or Enterobacter. In another foreseen version ofthe invention, the mixture of microorganisms is a community of naturalmicroorganisms that form a biofilm isolated from the environment.

In a preferred embodiment of this invention, the bioreactor is a fixedbed aerated column, a fluidized bed reactor or a trickling filter. In aforeseen version of the invention, the agitation of the culture mediumin the bioreactor is performed by recycling the culture medium with apump. In another foreseen version of the invention, the temperaturecontrol is performed by a temperature exchanger.

In a preferred embodiment of this invention, the desorbent agentemployed to remove the metals from the attached biofilm and recover thebiosorption capability of the microorganisms, can be: sulfuric acid,hydrochloric acid, phosphoric acid or citric acid.

In an alternative embodiment of this invention, the colonization of thefixed bed by microorganisms is performed alternately and previously inan additional bioreactor that is in a different place from the plant, topack the colonized fixed bed in the biosorption bioreactor when startingthe functioning of the treatment plant or to replace the microbial filmwhen, after many biosorption, desorption and neutralization cycles, itsmetal removal capacity begins to diminish.

In a preferred embodiment of this invention, the first stage ofprecipitation by pH rising pretreatment comprises:

letting the effluent loaded with metals in a neutralization tank, withstirrer, to which a sodium hydroxide solution is added, according to theparticular requirements of the industrial liquid waste to be treated;once neutralized, leading the flow to a settling tank to accumulate thesettling compounds to be eliminated subsequently;leading the supernatant into a feed tank to pass it subsequently to thebioreactors, where the biosorption process is performed; andincorporating, at the beginning of the process, the solution loaded withmetals from the subsequent stage of desorption of the bioreactors, atthe neutralization reactor.

In an additional embodiment, the settling compounds generated in thispre-treatment are subjected also to dewatering by a mechanical system,just like a press-filter or a centrifuge.

In another preferred embodiment, the first stage of pre-treatment bysolvent extraction comprehends:

contacting in a mixer-settler tank the organic phase constituted by adiluted extractant in an apolar diluent with the effluent to be treated;agitating properly the resulting mix;after a settling stage, obtaining the raffinate, corresponding to anaqueous, low metal concentrated solution and an organic, loaded withmetals solution;letting the raffinate solution pass directly to the final process ofbiosorption; meanwhile and simultaneously, contacting the organicsolution containing the metals in a second mixer-settler tank with ahard acid solution (stripping solution);after agitation and settling, concentrating the metals in the stripliquor and regenerate the organic phase which is recycled to the initialmixer-settler tank; andincorporating the solution loaded with metals from the subsequent stageof desorption of the bioreactors by a conduit at the inlet of the liquidindustrial waste to the process.

In another preferred embodiment, the first stage of pre-treatment bysolvent extraction on emulsified liquid membranes comprehends:

preparing in a tank of the first emulsion, agitating energetically thestripping solution along with the organic phase, constituted by anextractant and tensoactive diluted in a diluent;contacting in a mixer-settler tank, the first emulsion with the effluentto be treated, performing moderated agitation, which originates a doubleemulsion;settling the three-phased system, after contacting the double emulsionto separate the first emulsion loaded with raffinate metals, which passto the biosorption stage;performing, besides, in the tank the breakdown of the emulsion, tofinally obtain the strip liquor and an organic solution that is recycledto the tank to prepare the first emulsion; andincorporating the solution loaded with metals from the subsequent stageof desorption of the bioreactors by a conduit at the inlet of the liquidindustrial waste to the process.

Particularly, the surfactant of tensoactive is sorbitan monooleate.Thus, the diluent is selected from the group constituted by aviationkerosene, n-heptane y n-hexane and the extractant is selected from thegroup constituted by 5-dodecylsalicylaldoxime and 2-ethylhexylphosphonicacid-mono-2-ethyl hexyl ester.

In another foreseen version of the present invention, the method alsocomprehends, between precipitation by pH rising and biosorption, achitosan binding stage. In a preferred embodiment of the presentinvention, the chitosan binding stage comprehends:

providing of at least two columns filled with chitosan;leading the pre-treated water with a pH higher than 3, essential for theprocess based on chitosan adsorption, to a first column of said at leasttwo columns and from said first column the solution to be led to one ofthe bioreactors of biosorption is obtained; meanwhile a second column ofsaid at least two columns, with a full adsorption capacity, is kept;when the adsorption capacity of said first column gets saturated, thepre-treated water must be led to said second column of said at least twocolumns, that were kept, now from said second column the solution to beled to one of the bioreactors of biosorption is obtained;subjecting said first column, meanwhile and simultaneously, to atreatment of desorption and neutralization to regenerate the chitosanadsorption capacity, said desorption is performed by adding a solutionwith a desorbent agent, as an acid solution, obtaining an acid solutionloaded with metal ions, which is led to the beginning of the process,mixing it with the effluent entering to the pre-treatment;performing, finally, the neutralization of said first column, adding abase solution to set the pH value close to the neutral point in order toimprove its adsorption capacity; andrepeating the previous procedure, performing a rotation of said at leasttwo columns when that one of said at least two columns, that receivesthe pre-treated effluent, gets saturated again, in which said that oneof said at least two columns can be said first column or said secondcolumn.

A second main object of the invention is a plant for the metals removalby biosorption from mining or industrial effluents that comprehends, atleast:

an inlet for the intake of the liquid industrial waste or mine drainageand inlet to the pre-treatment system;a pre-treatment system to reduce the metals load from a liquidindustrial waste or mine drainage to concentrations that can be treatedby the following biosorption system, selecting among precipitation by pHrising, solvent extraction or solvent extraction on emulsifiedmembranes;a conduit to lead the water of the biosorption system;a biosorption system;a conduit to lead the desorption solution of the biosorption system tothe inlet for the intaking of the liquid industrial waste or minedrainage and the entering to the pre-treatment system; anda conduit for the discharge of the water treated by the biosorptionsystem

In a preferred embodiment of this invention, the plant for the removalof metals comprehends:

a group of bioreactors, constituted by, at least, one fixed bedbioreactor, which packing material has been colonized with a biofilmformed by a microbial culture or a mixture of microorganisms with thecapacity of binding metals by biosorption;an acid mixer tank connected to the bioreactor to add the acid as adesorption agent; anda base mixer tank connected to said at least one bioreactor to add abase solution that permits the residual acid to be neutralized afterdesorption.

In other preferred embodiment of this invention, the plant for theremoval of metals comprehends:

a group of bioreactors, constituted by at least two fixed bedbioreactors, which packing material has been colonized with a biofilmformed by a microbial culture or a mixture of microorganisms with thecapacity of binding metals by biosorption in which said at least of twobioreactors are connected in such a way that allows a first reactor ofsaid at least of two bioreactors to perform the removal of metals bybiosorption of the solution from the pretreatment, while, a secondbioreactor of said at least of two bioreactors with a full biosorptioncapacity is kept or subjected to desorption and neutralization;an acid mixer tank connected to each of said bioreactors to add the acidas a desorption agent, anda base mixer tank connected to each one of said bioreactors to add abase solution that allows the residual acid neutralization after thedesorption.

In another preferred embodiment of this invention, the plant for theremoval of metals comprehends:

a group of bioreactors, constituted by at least three fixed bedbioreactors, which packing material has been colonized with a biofilmformed by a microbial culture or a mixture of microorganisms with thecapacity of binding metals by biosorption in which said at least threebioreactors are connected in a way that allows the connection in seriesof two of them to perform the removal of metals by biosorption of thesolution from the pre-treatment; meanwhile, a third bioreactor of saidat least of three bioreactors with a full biosorption capacity is keptor is subjected to desorption and neutralization;an acid mixer tank connected to each of said bioreactors to add the acidas a desorption agent; anda base mixer tank connected to each one of said bioreactors to add abase solution that allows the residual acid to be neutralized afterdesorption.

In other preferred embodiment of this invention, the plant for theremoval of metals comprehends also:

a base storage tank connected to the base mixer tank; andan acid storage tank connected to the acid mixer tank.

In other preferred embodiment of this invention, each one of thebioreactors of the group of bioreactors is a fixed bed aerated column,fluidized bed reactor or trickling filter. In a foreseen version of theinvention, the agitation in each one of the bioreactors of the group ofbioreactors is performed by a recycling pump. In another foreseenversion of the invention, the plant also comprehends a culture mediumpreparation tank connected to the group of bioreactors. In otherforeseen version of the invention, the plant also comprehends a heatexchanger connected to the recycling of the culture medium that allowsto keep the temperature within each one of the bioreactors of the groupof bioreactors during the colonization with the biofilm of the fixed bedsupport stage. In a preferred embodiment, the heat exchanger employed tocontrol the temperature in each one of the bioreactors of the group ofbioreactors is a plate heat exchanger or a tube heat exchanger. In otherpreferred embodiment the plant comprehends also a medium to provide anadequate aeration of the culture, during the stage of colonization withthe biofilm of the fixed bed support material within the group ofbioreactors.

According to an alternative embodiment of this invention, the plant alsocomprehends an additional bioreactor located in a different place fromthe plant, in which is previously performed the fixed bed colonizationby microorganisms to, subsequently, pack it in each one of thebioreactors of the group of biosorption bioreactors by the beginning ofthe functioning of the plant or to replace the microbial film when,after many biosorption, desorption and neutralization cycles, its metalsremoval capacity begins to diminish.

In a preferred embodiment of the invention the plant for the removal ofmetals has a precipitation by pH rising pre-treatment system thatcomprehends, at least:

a neutralization reactor with a stirrer;a settling tank; anda feed tank (also called buffer tank)

In other preferred embodiment of the invention, the plant for theremoval of metals presents a solvent extraction pre-treatment systemthat comprehends at least:

a first stirrer tank to mix the extractant and the diluenta first mixer-settler tank;a second mixer-settler tank; andan acid mixer tank.

In an additional preferred embodiment of this invention, the watertreatment plant for the metals removal has a solvent extraction onemulsified liquid membranes pre-treatment system that comprehends atleast:

a stirrer tank to perform the solvent preparation;a first stirrer tank to prepare the first emulsion;a second stirrer tank to prepare the stripping solution; anda mixer-settler tank to separate the first raffinate emulsion.

According to an additional embodiment of this invention, the plant alsocomprehends a chitosan binding stage, between precipitation by pH risingand biosorption. In a particular application, the chitosan binding stagecomprehends, at least, two adsorption columns filled with chitosan.

In a preferred particular embodiment of this invention, the plant forthe metals removal can be built inside of a shipping-type mobilecontainer, provided of inner walls, a ceiling and a thermically isolatedfloor and with a washable covering and with, at least, one door and onewindow and an air conditioning system to control the inner temperaturein places with different weather conditions, which allows to transportit and evaluate the performance of said plant.

DESCRIPTION OF THE DRAWINGS

FIG. 1:

This Figure shows the flow sheet of a bioremediation process thatemploys a precipitation by pH rising pre-treatment stage.

FIG. 2:

This Figure shows the flow sheet of a bioremediation process thatemploys a solvent extraction pre-treatment stage.

FIG. 3:

This Figure shows the flow sheet of a bioremediation process thatemploys a solvent extraction on emulsified liquid membranespre-treatment stage.

FIG. 4:

This Figure shows the flow sheet of a bioremediation process thatemploys a precipitation by pH rising and adsorption on chitosanpre-treatment stage.

The following detailed description illustrates some concreteapplications of the invention; however, it does not intend to restrainthe frame nor the reaches of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the flow sheet of a bioremediation process that employs aprecipitation by pH rising pre-treatment stage.

The process consists of a treatment system for metal-polluted watersfrom the mining-metallurgic industry, by pre-treatment of thephysical-chemical type and a biological treatment based on metalsbiosorption that, basically, consists of the metals removal by means ofmicroorganisms.

The process begins with a pre-treatment stage. The liquid industrialwaste from a mining company, a metallurgic activity and from anindustrial activity, polluted with metals, is introduced by conduit 1 toa neutralization reactor 2, with stirrer, to which is added by conduit 3a sodium hydroxide solution (e.g. NaOH 50%) stored in a tank 4,according to the requirements of the features of liquid industrial wasteor mine drainage for their treatment. Once the liquid industrial wastehas been neutralized, conduit 5 leads the liquid along with itsprecipitate to a settler tank 6 to accumulate the settling compoundsthat will be, subsequently, eliminated through conduit 7. Thesupernatant is fed by conduit 8 to a feed tank 9, also called buffertank, and then, passed through conduit 10 to the stage where thebiosorption process is developed.

The biosorption process consists of three stages called: culture,biosorption and desorption. The culture stage is necessary to form themicrobial film in the fixed bed bioreactors, which present the metalremoval by biosorption capability. The culture is needed not only forthe initial formation of the microbial film, but also to replace themicrobial film when its metals removal capacity begins to diminish,which is forward explained in detail.

Biosorption Stage

The biosorption stage refers to the removal of the metal ions in theliquid industrial waste or mine drainage from the pre-treatment stagethrough conduit 10. This stage is performed by using two fixed bedbioreactors in series with microbial films. The first bioreactor isemployed to obtain a coarse metals removal and the second bioreactorallows an additional reduction of the metals concentration. Therefore,to obtain a continuous treatment system of the continuous type, at leastthree bioreactors are required. These bioreactors function,sequentially, according to three possible combinations (called forwardcase 1, case 2, and case 3).

In case 1, pre-treated water coming from conduit 10 is led by conduit 11to conduit 12 to feed fixed bed bioreactor 13 with attachedmicroorganisms, in which metals removal by biosorption to the attachedmicroorganisms is produced. Water treated in bioreactor 13 is led byconduits 14, 15 and 16 to bioreactor 17, from which the treated effluentis obtained and led by conduit 18 to the discharge of the plant 19.

Case 2 occurs when bioreactor 13 gets saturated with metals. In thiscase, bioreactor 13 is taken away from the biosorption process and isreplaced by bioreactor 17, that fills the place of the first bioreactor,while bioreactor 17 is replaced by bioreactor 20. For this purpose,pre-treated water from conduit 10 is led by conduit 21 to conduit 16 tofeed fixed bed bioreactor 17 with attached microorganisms. Water treatedin bioreactor 17 is led by conduits 18, 22 and 23 to bioreactor 20, fromwhich treated effluent is obtained and led, by conduit 24, to thedischarge of the plant 19.

Case 3 occurs when bioreactor 17 gets saturated with metals. In thiscase, bioreactor 17 is taken away from the biosorption process and isreplaced by bioreactor 20, that fills the place of the first bioreactor,while bioreactor 20 is replaced by bioreactor 13. For this purpose,pre-treated water form conduit 10 is led by conduit 25 to conduit 23 tofeed fixed bed bioreactor 20 with attached microorganisms. Water treatedin bioreactor 20 is led by conduits 24, 26, and 12 to bioreactor 13,from which treated effluent is obtained and led, by conduit 14, to thedischarge of the plant 19.

Once bioreactor 20 gets saturated with metals, case 1, alreadyexplained, starts again.

Desorption and Neutralization Stages

During the time bioreactor 13 is out of the biosorption process (case2), it is subjected to the desorption stage that allows to elute themetal ions from the bioreactor and regenerate the metals bindingcapacity of the microorganisms attached to the support. This isperformed by treating bioreactor 13 with an acid solution and,subsequently, with a base solution to neutralize the acid in thebioreactor. To prepare the acid solution, concentrated sulfuric acid(e.g. H₂SO₄ 95-97%) stored in tank 27, is led by conduit 28 along withwater with low metals concentration (or treated by this process) thatenters to the plant by the feeding conduit 29 and is led by conduit 30to an acid mixer tank 31. The acid mixed solution is transported byconduits 32, 33 and 12 to bioreactor 13. The solution loaded with metalsis taken away, after the desorption stage, from bioreactor 13 byconduits 34, 35 and 36 and is incorporated in neutralization reactor 2.Once desorption is finished, the pH in bioreactor 13 is neutralized byusing a base solution. To prepare the base solution, a concentratedsodium hydroxide solution (e.g. NaOH 50%) stored in tank 4 is led byconduit 37 and mixed with the low metals concentrated water (or treatedby this process) from conduit 29. This mixture is led by conduit 38 to asodium hydroxide mixer tank 39. The mixed base solution is transportedby conduits 40, 33 and 12 to bioreactor 13. The neutralizing solution istaken away from bioreactor 13 by conduits 34 and 35 and is discharged atthe exit of the plant by conduit 19.

During the time bioreactor 17 is out of the biosorption process (case3), it is subjected to the desorption stage, that allows the adsorbedmetal ions to be eluted from the bioreactor and regenerate the metalsbinding capacity of the microorganisms attached to the support. This isperformed by treating bioreactor 17 with an acid solution and,subsequently, with a base solution to neutralize the acid in thebioreactor. For this purpose, an acid solution is led to bioreactor 17.To prepare the acid solution, concentrated sulfuric acid (e.g. H₂SO₄95-97%) stored in tank 27 is led by conduit 28 along with low metalsconcentrated water (or treated by this process) that flows into theplant by the feeding conduit 29 and is led by conduit 30 to an acidmixer tank 31. The acid mixed solution is transported by conduits 32, 41and 16 to bioreactor 17. The solution loaded with metals, after thedesorption stage is taken away from bioreactor 17 by conduits 42, 35 and36 and is incorporated in the neutralizing reactor 2. Once thedesorption is finished, the pH in bioreactor 17 is neutralized by usinga base solution. To prepare the base solution, a concentrated sodiumhydroxide solution (e.g. NaOH 50%) stored in tank 4 is led by conduit 37and is mixed with low metals concentrated water (or treated by thisprocess) from conduit 29. This mixture is led by conduit 38 to a sodiumhydroxide mixer tank 39. The mixed base solution is transported byconduits 40, 41 and 16 to bioreactor 17. The neutralizing solution istaken away from bioreactor 17 by conduits 42 and 35 and is discharged atthe exit of the plant by conduit 19.

During the time bioreactor 20 is out of the biosorption process (case1), it is subjected to the desorption stage, that allows adsorbed metalions to be eluted from the bioreactor and regenerate the metals bindingcapacity of the microorganisms attached to the support. This isperformed by treating bioreactor 20 with an acid solution and,subsequently, with a base solution to neutralize the acid in thebioreactor. For this purpose, an acid solution is led to bioreactor 20.To prepare the acid solution, concentrated sulfuric acid (e.g. H₂SO₄95-97%) stored in tank 27 is led by conduit 28 and water with low metalsconcentration (or treated by this process) entering to the plant by thefeeding conduit 29 and is led, by conduit 30, to an acid mixer tank 31.The acid mixed solution is transported by conduits 32, 43 and 23 tobioreactor 20. The solution loaded with metals, after the desorptionstage, is taken away from bioreactor 20 by conduits 44, 35 and 36 and isincorporated in the neutralizing reactor 2. Once the desorption isfinished, the pH in bioreactor 20 is neutralized by using a basesolution. To prepare the base solution, a concentrated sodium hydroxidesolution (e.g. NaOH 50%) stored in tank 4 is led by conduit 37 and ismixed with low metals concentrated water (or treated by this process)from conduit 29. This mixture is led by conduit 38 to a sodium hydroxidemixer tank 39. The mixed base solution is transported by conduits 40, 43and 23 to bioreactor 20. The neutralizing solution is taken away frombioreactor 20 by conduits 44 and 35 and is discharged at the exit of theplant by conduit 19.

Culture Stage of the Attached Microorganisms on the Fixed Bed ofBioreactors

Biosorption occurs in bioreactors 13, 17 and 20 by the action ofmicroorganisms attached to the support or fixed bed. Therefore, whenstarting the functioning of the treatment method, colonization of thefixed bed or support by microorganisms with the capacity of bindingmetals (such as microorganisms of the type of Bacillus, Pseudomonas,Klebsiella, Enterobacter or mixtures of microorganisms that formbiofilms isolated from the natural environments). Thus, the microbialbiofilm must be replaced once its metals removal capacity, after manybiosorption, desorption and neutralization cycles, begins to diminish.In this last case, the fixed bed recolonization is performed in thebioreactor that has already finished the biosorption and neutralizationphase.

The attaching microorganisms culture in bioreactor 13 begins bypreparing the culture medium containing all the nutrients for thegrowing of the attaching microorganism in the culture medium preparationtank 45. The recently prepared culture medium is inoculated with theattaching microorganism and led to bioreactor 13 by conduits 46, 47 and48. Then, the inoculated culture medium is subjected to recycling byconduits 49, 47 and 48. During the recycling, the liquid is passedthrough by means of a heat exchange system 50 that works by a water bath51, that permits to keep the temperature stable inside of the bioreactorwith the purpose of achieving the optimal conditions for the growing andformation of the microbial biofilm of the attaching microorganism (e.g.28° C.). This heat exchange system includes a heater 52 to raise thetemperature at the beginning of the culture and a cooling by circulatingwater (to dissipate the heat produced by the growing of themicroorganism) that flows into the heat exchange system 50 by conduit 53and is taken away from it by conduit 54. To oxygenate the culture duringits growing, air is led from the air compressor 55 by conduits 56 and 57to bioreactor 13. A high oxygen transference is achieved bysynchronizing the recycling of the culture medium that enters to thebioreactor by conduit 48 and the air entering by conduit 57 by means ofthe application of an air injector that is immersed in the liquid columnand above the support material of the fixed bed bioreactor. The culturewith medium recycling, aeration and temperature control is kept untilthe support material is colonized by the attaching microorganism (e.g. 8to 20 hours of culture). Once the culture is finished, the exhaustedculture medium of bioreactor 13 is taken away by conduits 34 and 35 andis discharged at the exit of the plant by conduit 19. Bioreactor 13 isleft to stand for 24 hours, after that it is ready to start abiosorption, desorption and neutralization cycle.

Thus, the attaching microorganisms culture in bioreactor 17 starts bypreparing the culture medium in the preparation of culture medium tank45. The recently prepared culture medium is inoculated with theattaching microorganism and is led to bioreactor 17 by conduits 46, 47and 58. After that, the inoculated culture medium is subjected torecycling by conduits 59, 47 and 58. During recycling, the liquid ispassed through a heat exchange system 50. To oxygenate the cultureduring its growing, air is led from the air compressor 55 by conduits 56and 60 to bioreactor 17. A high oxygen transference is achieved bysynchronizing the recycling of the culture medium that enters to thebioreactor by conduit 58 and the air entering by conduit 60 by means ofthe application of an air injector that is immersed in the liquid columnand above the support material of the fixed bed bioreactor. The culturewith recycling of the culture medium, aeration and temperature controlis kept until the support material is colonized by the attachingmicroorganism (e.g. 8 a 20 hours of culture). Once the culture isfinished, the exhausted culture medium in bioreactor 17 is taken away byconduits 42 and 35 and discharged at the exit of the plant by conduit19. Bioreactor 17 is left to stand for 24 hours, after that it is readyto begin a biosorption, desorption and neutralization cycle.

The attaching microorganisms culture in bioreactor 20 starts bypreparing the culture medium in the culture medium preparation tank 45.The recently prepared culture medium is inoculated with the attachingmicroorganism and led to bioreactor 20 by conduits 46, 47 and 61. Afterthat, the inoculated culture medium is subjected to recycling byconduits 62, 47 and 61. During recycling, the liquid is passed through aheat exchange system 50. To oxygenate the culture during its growing airis led from the air compressor 55 by conduits 56 and 63 to bioreactor20. A high oxygen transference is achieved by synchronizing the culturemedium recycling that enters to the bioreactor by conduit 61 and the airentering by conduit 63 by means of the application of an air injectorimmersed in the liquid column and above the support material of thefixed bed bioreactor. The culture with recycling of culture medium,aeration and temperature control is kept until the support material iscolonized by attaching microorganisms (e.g. 8 to 20 hours of culture.)Once the culture is finished, the exhausted culture medium in bioreactor20 is taken away by conduits 44 and 35 and discharged at the exit of theplant by conduit 19. Bioreactor 20 is left to stand for 24 hours, afterthat it is ready to start a biosorption, desorption and neutralizationcycle.

FIG. 2 shows a flow sheet of a bioremediation process that employs apre-treatment by solvent extraction stage.

The liquid industrial waste of a mining company, a metallurgic activity,or an industrial activity, contaminated with metals, is introduced byconduit 64 into a mixer-settler extraction tank 65 where it is contactedwith an organic type liquid phase called “solvent” prepared in reactor66. To said reactor enter, by conduit 67, an acid extractant compound(e.g. 5-dodecylsalicylaldoxime, 2-ethylhexylphosphonic acid-mono-2-ethylhexyl ester) and a diluent substance (e.g. aviation Kerosene, n-heptane,n-hexane) by conduit 68. These substances are mixed in differentproportions. This solvent is transported to the mixer-settler tank 65 byconduits 69 and 70. The mixer-settler tank consists of a mixing bymechanic agitation area, followed by a settling area where the phasesseparation occurs. The liquid industrial waste of mine drainage and thesolvent mix are agitated properly in the mixing area (e.g. 120 rpm) ofthe mixer-settler tank 65 and then, by overflowing, it is led to thesettling area, where a raffinate solution corresponding to an aqueoussolution with low concentration of metals and an organic solution loadedwith metals are obtained. The raffinate solution enters directly to thefinal process of biosorption by conduit 10 (above explained), while theorganic solution containing the metals is transported by conduit 71 to asecond mixer-settler stripping tank 72. In the mixer-settler tank 72,the organic solution loaded with metals is contacted with a hard acidsolution (stripping solution) added by conduit 73 and from the acidmixer tank 74 in which concentrated sulfuric acid and the water with lowmetals content (or treated by this process) from conduits 29 and 75 aremixed. The concentrated sulfuric acid is kept in tank 27 and transportedby conduit 76 to the mixing tank 74. In the mixing area of themixer-settler tank 72 by mechanic agitation (e.g. 120 rpm) the organicphase containing the metals is mixed with the acid sulfuric solution,and then, the mixture is passed through overflowing to the settlingarea. As a result of this contact, it is obtained, on one hand, anaqueous phase less acid where metals are concentrated; this phase iscalled “strip liquor” and comes out from the plant by conduit 77 to anpossible subsequent process of metals recovery and purification. On theother hand, from the mixer-settler tank 72 the organic phase isregenerated and recycled to tank 65 by conduits 78 and 70.

The solution loaded with metals, from the desorption stage of thebioreactors is incorporated by conduit 36 to the same level as conduit64 of entrance to the process for the liquid industrial waste.

FIG. 3 shows the flow sheet of a bioremediation process that employs apre-treatment by solvent extraction stage on emulsified liquidmembranes.

In tank 81 is performed the preparation of the primary emulsion, byagitating energetically (e.g. 1200 rpm) the stripping solution preparedin reactor 86 and transported by conduit 89, with the organic phaseprepared in reactor 82 and transported by conduit 90. The organic phaseis compounded by an extractant (e.g. 5-dodecylsalicylaldoxime or2-ethylhexylphosphonic acid-mono-2-ethylhexyl ester) and a surfactant ortensoactive compound (e.g. sorbitan monooleate) dissolved in a diluent(e.g. aviation kerosene, n-hexane, n-heptane) led to reactor 82 byconduits 83, 84 and 85, respectively. The stripping solution is preparedin reactor 86 by mixing concentrated sulfuric acid, stored in tank 27,added by conduit 87 and water with low metal concentration (or treatedby this process) transported to reactor 86 by conduits 29 and 88.

The liquid industrial waste of a mining company, a metallurgic activity,or an industrial activity, contaminated with metals, is introduced byconduit 79 into a mixer-settler extraction tank 80 where it is contactedwith the primary emulsion, introduced by conduit 91, performing a mildagitation (e.g. 200 rpm) in the mixing area where a double emulsion ofthe type water/oil/water is produced. After the contact of the doubleemulsion in the mixing area of the mixer-settler tank 80, the mixture istransported by overflowing to the settling area of reactor 80, where thefirst emulsion loaded with metals is separated from the raffinatesolution, which is passed to the biosorption stage (above explained) byconduit 10. On the other hand, primary emulsion containing metals is ledby conduit 92 to reactor 93 to proceed to its breakdown (e.g. bycentrifugation, by heating or, by electric potential). From thisbreakdown of the primary emulsion is finally obtained the strip liquorthat comes out from the plant by conduit 94 to a subsequent possibleprocess of recovering and purification of metals and an organic solutionthat is recycled to tank 81 by conduit 95 for a new preparation of theprimary emulsion. The solution loaded with metals, coming from thebioreactors desorption stage is incorporated by conduit 36 to the samelevel as the conduit 79 of entrance to the process for the liquidindustrial waste.

FIG. 4 shows the flow sheet of a bioremediation process that employs acombined pre-treatment stage of precipitation by pH rising andadsorption on chitosan.

The preliminary stage starts by flowing the liquid industrial waste froma mining activity, a metallurgic activity or an industrial activity,polluted with metals, by conduit 96 into a stirred mixer tank 97 towhich is added by conduits 98 and 99 a NaOH solution (e.g. NaOH 50%),stored inside of tank 4 with the purpose of keeping the pH inside oftank 97 in a value higher or equal to 3, when necessary (pH<3). Onceneutralized the liquid industrial waste, conduit 100 passes the liquidwith its precipitate to a settler tank 101 to accumulate the settlingcompounds, subsequently eliminated by conduit 102. The supernatant isfed by conduit 103 to a feed tank 104, to pass then by conduit 105 tothe columns of chitosan adsorption, a natural polymer extracted aschitin from the shells of many different animals (e.g. prawns,crustaceans, insects) and subsequently modified into chitosan bychemical reaction of deacetylation. These columns work in a regimeconstituted by two stages called adsorption and desorption. Theadsorption stage corresponds to the removal of the metal ions in theflow from conduit 105, by a physical-chemical process of adsorption ofthese ions with chitosan. The desorption stage allows the adsorbed metalions to be eluted from the columns to regenerate the metal bindingcapacity of the chitosan by means of a concentrated mineral acidstreatment (e.g. sulfuric acid, nitric acid or hydrochloric acid)followed by an alkalinization of the polymer by sodium hydroxide toeliminate the excess of acidity possibly retained by the polymer duringthe desorption stage. While a column is in the adsorption stage, theother one is in the desorption stage and vice versa.

In the first case, the water from conduit 105 is led by conduit 106 toconduit 107 to feed column 108 packed with chitosan in which the partialremoval of metals is produced. The water treated in column 108 is led byconduits 109 and 110 to the biosorption stage. The second case occurswhen the saturation with metals of column 108 is produced. In thissituation, column 108 is taken away from the adsorption process andreplaced by column 110. For this purpose, the water from conduit 105 isled by conduit 111 to conduit 112 to feed column 110 packed withchitosan. The pre-treated water in column 110 is led by conduits 113 and10 to the biosorption stage (above explained).

While column 108 is out of the adsorption process (second case) it issubjected to the desorption stage. This is performed by treating column108 with an acid solution and, subsequently, with a base solution toneutralize the acid in the column. To prepare the acid solution,concentrated sulfuric acid (e.g. H₂SO₄ 95-97%) stored in tank 27, is ledby conduit 114 along with drinking water entering by the feeding conduit115 and led by conduit 116 to an acid mixer tank 117. The acid mixedsolution is transported by conduits 118, 119 and 107 to column 108. Thesolution loaded with metals, after the desorption stage is taken awayfrom column 108 by conduits 120 and 121 and is incorporated in theneutralization reactor 97. Once the desorption is finished the pH incolumn 108 is neutralized by a base solution. To prepare said basesolution, a concentrated NaOH solution (e.g. NaOH 50%) is stored in tank4, led by conduits 98 and 122, and mixed with drinking water coming formconduits 115 and 123 in the mixer tank 124. The base solution obtainedis transported by conduits 125, 126 and 107 to column 108. Theneutralization solution is taken away from column 108 by conduits 109and 110.

While column 110 is out of the adsorption process (first case) it issubjected to the desorption stage. This is performed by treating column110 with an acid solution and, subsequently, with a base solution toneutralize the acid in the column. To prepare the acid solution,concentrated sulfuric acid (e.g. H₂SO₄ 95-97%) stored in tank 27, is ledby conduit 114 along with drinking water entering by the feeding conduit115 and led by conduit 116 to an acid mixer tank 117. The acid mixedsolution is transported by conduits 118, 127 and 112 to column 110. Thesolution loaded with metals, after the desorption stage is taken awayfrom column 110 by conduits 128 and 121 and is incorporated in theneutralization reactor 97. Once the desorption is finished the pH incolumn 110 is neutralized by a base solution. To prepare said basesolution, a concentrated NaOH solution (e.g. NaOH 50%) stored in tank 4is led by conduits 98 and 122 and mixed with drinking water coming formconduits 115 and 123 in the mixer tank 124. The base solution obtainedis transported by conduits 125, 129 and 112 to column 110. Theneutralization solution is taken away from column 110 by conduits 113and 10.

The solution loaded with metals coming from the bioreactors desorptionstage is incorporated by conduit 36 by conduit 96 of entrance to theprocess for the liquid industrial waste.

As an example, a semi pilot plant is built to perform tests in place ofthe bioremediation process of water useful to biologically remove heavymetals using attached microorganisms, designed for the continuoustreatment of a 1 m³/day flow rate. This semi pilot plant, according tothe flow sheet explained in FIG. 1, is installed inside of a 2.5×6.0metres container, which is provided of internal walls, ceiling and athermically isolated floor with a washable covering. The frontal wall ofthe container has one door and two windows. In a lateral wall an airconditioning system is installed in order to control the innertemperature in places with different weather conditions. This allows totransport and evaluate the plant in the place where liquid residues aregenerated in mining and manufactory companies. This allows to makedecisions about special pre-treatments, depending on the contaminationlevel of each company, and make escalation projections for an industrialtype of plant. The semi pilot plant is provided of the followingreactors and bioreactors, according to the flow sheet in FIG. 1:

-   -   neutralization reactor with stirrer (250 litres)    -   settling tank (250 litres)    -   feed tank (also called buffer tank) (250 litres)    -   base mixer tank with stirrer (100 litres)    -   acid mixer tank (250 litres)    -   culture medium preparation tank with stirrer (250 litres)    -   three fixed bed bioreactors with metals removal by biosorption        capability (100 litres each)    -   heat exchange system

The four pumps are installed for the conveyance of the liquid industrialwaste or mine drainage to be treated at the different stages of theprocess, the culture medium recycling pump for the three bioreactors,the dosing pump for NaOH and H₂SO₄, the hand-operated and solenoidvalves, an air compressor and the piping and conduits, according to theflow sheet in FIG. 1. Thus, electrical connections and automatizationand monitoring system SNAP I/O of Opto22 of the processes involved inthe bioremediation plant are installed.

In an external ware house the following reagent vessels are located:

-   -   NaOH (50 litres) storage tank    -   H₂SO₄ tank (50 litres) storage tank

The following numerical values, which should not be considered asrestrictions, are quoted in order to provide an example of the resultsobtained when applying the semi pilot plant to different miningeffluents that present low pH values and high contents of dissolvedmetals:

For an affluent from a mining company and introduced to the plantthrough conduit 1:

pH=1.5-4.0Cu²⁺=20-300 mg/LFe³⁺=1-320 mg/LZn²⁺=6-80 mg/L

For a treated effluent, that is led to the discharge of the plant 19:

pH=6.0-6.5Cu²⁺=<1 mg/LFe³⁺=<5 mg/LZn²⁺=<3 mg/L

As an additional example of the application of this invention, atreatment plant for effluents with high metals concentration and low pHis described. Said plant is designed for the continuous treatment of a50 m3/day flow rate. The plant is provided of the following reactors andbioreactors, according to the flow sheet in FIG. 1:

-   -   neutralization reactor with stirrer (300 m³)    -   settling tank (300 m³)    -   feed tank (also called buffer tank) (300 m³)    -   base mixer tank with stirrer (120 m³)    -   acid mixer tank (120 m³)    -   culture medium preparation tank with stirrer (120 m³)    -   three fixed bed bioreactors with the metals removal by        biosorption capacity (120 m³ each)    -   heat exchange system

The four pumps are installed for the conveyance of the liquid industrialwaste or mine drainage to be treated at the different stages of theprocess, the culture medium recycling pump for the three bioreactors,the dosing pump for NaOH and H₂SO₄, the hand-operated and solenoidvalves, an air compressor and the piping and conduits, according to theflow sheet in FIG. 1. Thus, electrical connections and an automation andmonitoring system SNAP I/O of Opto22 of the processes involved in thebioremediation plant are installed.

Also, the following reagent vessels are built:

-   -   NaOH (60 m³) storage tank    -   H₂SO₄ (60 m³) storage tank

1. A method for the removal of metals by biosorption from mining orindustrial effluents which comprises: (a) subjecting the effluent to, atleast, one first stage of pre-treatment, selecting among: precipitationby pH rising, solvent extraction or solvent extraction on emulsifiedliquid membranes to reduce its load of metals to concentrations that canbe treated in the next stage of biosorption; and (b) subjecting theliquid that has been previously treated at the pre-treatment stage to asecond stage of continuous removal of metals by biosorption, in whichmicrobial biomass is grown and immobilized in a bioreactor, towardswhich the water to be treated is led and, finally, the metal ionsuptaken by the biomass are eluted.
 2. A method for the removal of metalsin accordance with claim 1, wherein said continuous metals removal bybiosorption stage comprises the steps of: (b1) providing of at least twofixed bed bioreactors, which packing material can be colonized with abiofilm formed by a microbial culture or a mixture of microorganismswith the metal binding by biosorption capability; (b2) always performthe colonization of the packing material of said at least twobioreactors using microorganisms when starting the functioning of thetreatment method, said colonization is performed by adding culturemedium to said at least two bioreactors, inoculating them with theattaching microorganism and subjecting the culture to aeration,agitation and temperature control for a suitable period of time toobtain the effective colonization of the support material of said atleast two bioreactors, once the culture is finished, the culture mediumis taken away and said at least two bioreactors are ready to be employedin the biosorption stage; (b3) leading the pre-treated water to a firstbioreactor of one of said at least two bioreactors from which one thetreated effluent is obtained and led to the discharge of the plant;meanwhile, a second bioreactor from one of said at least two bioreactorsthat presents full biosorption capacity, is kept; (b4) when thebiosorption capacity of said first bioreactor gets saturated, lead thepre-treated water to said second bioreactor that was kept, now from thislast one the treated effluent is obtained and lead to the discharge ofthe plant; (b5) subjecting said first bioreactor, meanwhile andsimultaneously, to a treatment of desorption and neutralization, toregenerate the biosorption capacity of the biofilm attached to thesupport material of said first bioreactor, said desorption is performedby adding a solution with a desorbent agent, just like an acid solution,that can displace the metals bound to the microorganisms, obtaining anacid solution loaded with metal ions, which is reused in a new processof desorption or is lead to the beginning of the process, mixing it withthe effluent entering to the pre-treatment; (b6) performing, finally,the neutralization of said first bioreactor, adding a base solution thatallows to set the pH value close to the neutral point, in order toimprove the biosorption capacity; and (b7) repeating from the previousstage b4, performing a rotation of said at least two bioreactors whenthat one of said at least two bioreactors that receives the pre-treatedeffluent gets saturated again, and where said that one of said at leasttwo bioreactors can be said first bioreactor or said second bioreactor;and (b8) performing the recolonization of the fixed bed usingmicroorganisms to replace the microbial film when, after manybiosorption, desorption and neutralization cycles, its metal removingcapacity begins to diminish, in this case, the recolonization of thefixed bed is performed in said first or second bioreactor that hasfinished the biosorption and neutralization phase, where saidcolonization is produced by adding culture medium to said first orsecond bioreactor, inoculating it with the attaching microorganism andsubjecting the culture to aeration, agitation and temperature controlfor a suitable period of time to obtain an effective colonization of thesupport material of said first or second bioreactor, once the culture isfinished, the culture medium is taken away and said first or secondbioreactor is ready to be used again in the biosorption stage.
 3. Amethod for the removal of metals in accordance with claim 1, whereinsaid continuous metal removing by biosorption stage comprises the stepsof: (b1) providing of at least three fixed bed bioreactors, whichpacking material can be colonized with a biofilm formed by a microbialculture or a mixture of microorganism with the capability of bindingmetals by biosorption; (b2) always perform the colonization of thepacking material of said at least three bioreactors using microorganismswhen starting the functioning of the treatment method, said colonizationis produced by adding culture medium to said at least three bioreactors,inoculating them with the attaching microorganism and subjecting theculture to aeration, agitation and temperature control for a suitableperiod of time to obtain the effective colonization of the supportmaterial of said at least three bioreactors, once the culture isfinished, the culture medium is taken away and said at least threebioreactors are ready to be used in the biosorption stage; (b3) leadingthe pre-treated water to a first bioreactor of said at least threebioreactors and from this one to a second bioreactor of said at leastthree bioreactors, connected in series, from this last one the treatedeffluent is obtained, and led to the discharge of the plant; meanwhile,a third bioreactor of said at least three bioreactors, that presents afull biosorption capacity, is kept; (b4) leading the pre-treated waterto said second bioreactor when the biosorption capacity of said firstbioreactor gets saturated and from this one to said third bioreactor,connected in series, that was kept, now from this last one is obtainedthe treated effluent that is led to the discharge of the plant; (b5)subjecting said first bioreactor, meanwhile and simultaneously, to adesorption and neutralization treatment, in order to regenerate thebiosorption capacity of the biofilm that is attached to the supportmaterial of said first bioreactor, said desorption is performed byadding a solution with a desorbent agent, just like an acid solution,that can displace the metals bound to the microorganisms, obtaining anacid solution loaded with metal ions, and which is reused in a newdesorption process or is led to the beginning of the process, mixing itwith the effluent entering to the pre-treatment; (b6) performing,finally, the neutralization of said first bioreactor, adding a basesolution to set the pH value close to the neutral point in order toimprove its biosorption capacity; (b7) repeating from previous stage b4performing a rotation of the bioreactors when that one reactor, fromsaid at least three bioreactors that receives the pre-treated effluent,gets saturated again, where that one bioreactor of said at least threebioreactors can be said first, second or third bioreactor; and (b8)performing the recolonization of the fixed bed by microorganisms toreplace the microbial film when, after many biosorption, desorption andneutralization cycles, its metal removing capacity begins to diminish;in this case, the recolonization of the fixed bed is performed in thesame bioreactor that has finished the biosorption and neutralizationstage; said colonization is performed by adding culture medium to saidbioreactor; the said colonization is performed by adding culture mediumto said bioreactor, inoculating it with the attaching microorganism andsubjecting the culture to aeration, agitation and temperature controlfor a suitable period of time to obtain an effective colonization of thesupport material of said bioreactor, once the culture is finished theculture medium is taken away and said bioreactor is ready to be usedagain in the biosorption stage;
 4. A method for the removal of metals inaccordance with claim 2, wherein said microbial culture is a bacterialor archaeal culture.
 5. A method for the removal of metals in accordancewith claim 4, wherein said culture of bacteria contains a population ofselected bacteria among the genus Bacillus, Pseudomonas, Klebsiella orEnterobacter.
 6. A method for the removal of metals in accordance withclaim 2, wherein said mixture of microorganisms is a community ofnatural microorganisms that form a biofilm isolated form theenvironment.
 7. A method for the removal of metals in accordance withclaim 2, wherein said bioreactor is a fixed bed aerated column.
 8. Amethod for the removal of metals in accordance with claim 2, whereinsaid bioreactor is a fluidized bed reactor.
 9. A method for the removalof metals in accordance with claim 2, wherein said bioreactor is atrickling filter.
 10. A method for the removal of metals in accordancewith claim 2, wherein said agitation is performed by recycling theculture medium with a pump.
 11. A method for the removal of metals inaccordance with claim 2, wherein said temperature control is performedby a temperature exchanger.
 12. A method for the removal of metals inaccordance with claim 2, wherein said desorbent agent can be; sulfuricacid, hydrochloric acid, phosphoric acid or citric acid.
 13. A methodfor the removal of metals in accordance with claim 2, wherein saidcolonization of the fixed bed by microorganisms is performed alternatelyand previously in an additional bioreactor that is in a different placefrom the plant, to pack it in the biosorption bioreactor when startingthe functioning of the treatment plant or to replace the microbial filmwhen, after many biosorption, desorption and neutralization cycles, itsmetal removal capacity begins to diminish.
 14. A method for the removalof metals in accordance with claim 3, wherein said microbial culture isa bacterial or archaeal culture.
 15. A method for the removal of metalsin accordance with claim 14, wherein said culture of bacteria contains apopulation of selected bacteria among the genus Bacillus, Pseudomonas,Klebsiella or Enterobacter.
 16. A method for the removal of metals inaccordance with claim 3, wherein said mixture of microorganisms is acommunity of natural microorganisms that form a biofilm isolated formthe environment.
 17. A method for the removal of metals in accordancewith claim 3, wherein said bioreactor is a fixed bed aerated column. 18.A method for the removal of metals in accordance with claim 3, whereinsaid bioreactor is a fluidized bed reactor.
 19. A method for the removalof metals in accordance with claim 3, wherein said bioreactor is atrickling filter.
 20. A method for the removal of metals in accordancewith claim 3, wherein said agitation is performed by recycling theculture medium with a pump.
 21. A method for the removal of metals inaccordance with claim 3, wherein said temperature control is performedby a temperature exchanger.
 22. A method for the removal of metals inaccordance with claim 3, wherein said desorbent agent can be: sulfuricacid, hydrochloric acid, phosphoric acid or citric acid.
 23. A methodfor the removal of metals in accordance with claim 3, wherein saidcolonization of the fixed bed by microorganisms is performed alternatelyand previously in an additional bioreactor that is in a different placefrom the plant, to pack it in the biosorption bioreactor when startingthe functioning of the treatment plant or to replace the microbial filmwhen, after many biosorption, desorption and neutralization cycles, itsmetal removal capacity begins to diminish.
 24. A method for the removalof metals in accordance with claim 1, wherein said first stage ofprecipitation by pH rising pre-treatment comprising the steps of:letting the effluent loaded with metals in a neutralization tank, withstirrer, to which a sodium hydroxide solution is added, according to theparticular requirements of the industrial liquid waste to be treated;once neutralized, leading the flow to a settling tank to accumulate thesettling compounds to be eliminated subsequently; leading thesupernatant into a feed tank to pass it subsequently to the bioreactors,where the biosorption process is performed; and incorporating, at thebeginning of the process, the solution loaded with metals from thesubsequent stage of desorption of the bioreactors, at the neutralizationreactor.
 25. A method for the removal of metals in accordance with claim24, wherein said settling compounds generated in this pre-treatment aresubjected also to dewatering by a mechanical system, just like a pressfilter or a centrifuge.
 26. A method for the removal of metals inaccordance with claim 24, wherein said method also comprises, betweenprecipitation by pH rising and biosorption, a chitosan binding stage.27. A method for the removal of metals in accordance with claim 26,wherein said chitosan binding stage comprises the steps of: providing ofat least two columns filled with chitosan; leading the pre-treated waterwith a pH higher than 3, essential for the process based on chitosanadsorption, to a first column of said at least two columns and from saidfirst column the solution to be led to one of the bioreactors ofbiosorption is obtained; meanwhile a second column of said at least twocolumns, with a full adsorption capacity, is kept; when the adsorptioncapacity of said first column gets saturated, the pre-treated water mustbe led to said second column of said at least two columns, that werekept, now from said second column the solution to be led to one of thebiosorption bioreactors is obtained; subjecting said first column,meanwhile and simultaneously, to a treatment of desorption andneutralization to regenerate the chitosan adsorption capacity, saiddesorption is performed by adding a solution with a desorbent agent,just as an acid solution, obtaining an acid solution loaded with metalions, which is led to the beginning of the process, mixing it with theeffluent entering to the pre-treatment; performing, finally, theneutralization of said first column, adding a base solution to set thepH value close to the neutral point in order to improve its adsorptioncapacity; and repeating the previous procedure, performing a rotation ofsaid at least two columns when that one of said at least two columns,that receives the pre-treated effluent, gets saturated again, in whichsaid that one of said at least two columns can be said first column orsaid second column.
 28. A plant for the metals removal by biosorptionfrom mining or industrial effluents, wherein said treatment plantcomprises at least: an inlet for the intake of the liquid industrialwaste or mine drainage and inlet to the pre-treatment system; apre-treatment system to reduce the metals load from a liquid industrialwaste or mine drainage to concentrations that can be treated by thefollowing biosorption system, selecting among precipitation by pHrising, solvent extraction or solvent extraction on emulsifiedmembranes; a conduit to lead the water of the biosorption system; abiosorption system; a conduit to lead the desorption solution of thebiosorption system to the inlet for the intaking of the liquidindustrial waste or mine drainage and the entering to the pre-treatmentsystem; and a conduit for the discharge of the water treated by thebiosorption system
 29. A plant for the metals removal by biosorptionfrom mining or industrial effluents in accordance with claim 28, whereinsaid biosorption system comprises: a group of bioreactors, constitutedby at least two fixed bed bioreactors, which packing material has beencolonized with a biofilm formed by a microbial culture or a mixture ofmicroorganisms with the capacity of binding metals by biosorption inwhich said at least of two bioreactors are connected in such a way thatallows a first reactor of said at least of two bioreactors to performthe removal of metals by biosorption of the solution from thepre-treatment, while, a second bioreactor of said at least of twobioreactors with a full biosorption capacity is kept or subjected todesorption and neutralization; an acid mixer tank connected to each ofsaid bioreactors to add the acid as a desorption agent, and a base mixertank connected to each one of said bioreactors to add a base solutionthat allows the residual acid neutralization after the desorption.
 30. Aplant for the metals removal by biosorption from mining or industrialeffluents in accordance with claim 28, wherein said biosorption systemcomprises: a group of bioreactors, constituted by at least three fixedbed bioreactors, which packing material has been colonized with abiofilm formed by a microbial culture or a mixture of microorganismswith the capacity of binding metals by biosorption in which said atleast three bioreactors are connected in a way that allows theconnection in series of two of them to perform the removal of metals bybiosorption of the solution from the pre-treatment; meanwhile, a thirdbioreactor of said at least of three bioreactors with a full biosorptioncapacity is kept or is subjected to desorption and neutralization; anacid mixer tank connected to each of said bioreactors to add the acid asa desorption agent; and a base mixer tank connected to each one of saidbioreactors to add a base solution that allows the residual acid to beneutralized after desorption.
 31. A plant for the metals removal bybiosorption from mining or industrial effluents in accordance with claim29, wherein each one of the bioreactors of said group of bioreactors isa fixed bed aerated column.
 32. A plant for the metals removal bybiosorption from mining or industrial effluents in accordance with claim29, wherein each one of the bioreactors of said group of bioreactors isa fluidized bed reactor.
 33. A plant for the metals removal bybiosorption from mining or industrial effluents in accordance with claim29, wherein each one of the bioreactors of said group of bioreactors isa or trickling filter.
 34. A plant for the metals removal by biosorptionfrom mining or industrial effluents in accordance with claim 29, whereinagitation in each one of the bioreactors of said group of bioreactors isperformed by a recycling pump.
 35. A plant for the metals removal bybiosorption from mining or industrial effluents in accordance with claim29, wherein said plant also comprehends a heat exchanger connected tothe recycling of the culture medium that allows to keep the temperaturewithin each one of the bioreactors of the group of bioreactors duringthe colonization with the biofilm of the fixed bed support stage.
 36. Aplant for the metals removal by biosorption from mining or industrialeffluents in accordance with claim 35, wherein said heat exchangeremployed to control the temperature in each one of the bioreactors ofthe group of bioreactors is a plate heat exchanger or a tube heatexchanger.
 37. A plant for the metals removal by biosorption from miningor industrial effluents in accordance with claim 29, wherein said plantcomprehends also a medium to provide an adequate aeration of theculture, during the stage of colonization with the biofilm of the fixedbed support material within the group of bioreactors.
 38. A plant forthe metals removal by biosorption from mining or industrial effluents inaccordance with claim 29, wherein said plant also comprehends anadditional bioreactor located in a different place from the plant, inwhich is previously performed the fixed bed colonization bymicroorganisms to, subsequently, pack it in each one of the bioreactorsof the group of biosorption bioreactors by the beginning of thefunctioning of the plant or to replace the microbial film when, aftermany biosorption, desorption and neutralization cycles, its metalsremoval capacity begins to diminish.
 39. A plant for the metals removalby biosorption from mining or industrial effluents in accordance withclaim 30, wherein each one of the bioreactors of said group ofbioreactors is a fixed bed aerated column.
 40. A plant for the metalsremoval by biosorption from mining or industrial effluents in accordancewith claim 30, wherein each one of the bioreactors of said group ofbioreactors is a fluidized bed reactor.
 41. A plant for the metalsremoval by biosorption from mining or industrial effluents in accordancewith claim 30, wherein each one of the bioreactors of said group ofbioreactors is a or trickling filter.
 42. A plant for the metals removalby biosorption from mining or industrial effluents in accordance withclaim 30, wherein agitation in each one of the bioreactors of said groupof bioreactors is performed by a recycling pump.
 43. A plant for themetals removal by biosorption from mining or industrial effluents inaccordance with claim 30, wherein said plant also comprehends a heatexchanger connected to the recycling of the culture medium that allowsto keep the temperature within each one of the bioreactors of the groupof bioreactors during the colonization with the biofilm of the fixed bedsupport stage.
 44. A plant for the metals removal by biosorption frommining or industrial effluents in accordance with claim 43, wherein saidheat exchanger employed to control the temperature in each one of thebioreactors of the group of bioreactors is a plate heat exchanger or atube heat exchanger.
 45. A plant for the metals removal by biosorptionfrom mining or industrial effluents in accordance with claim 30, whereinsaid plant comprehends also a medium to provide an adequate aeration ofthe culture, during the stage of colonization with the biofilm of thefixed bed support material within the group of bioreactors.
 46. A plantfor the metals removal by biosorption from mining or industrialeffluents in accordance with claim 30, wherein said plant alsocomprehends an additional bioreactor located in a different place fromthe plant, in which is previously performed the fixed bed colonizationby microorganisms to, subsequently, pack it in each one of thebioreactors of the group of biosorption bioreactors by the beginning ofthe functioning of the plant or to replace the microbial film when,after many biosorption, desorption and neutralization cycles, its metalsremoval capacity begins to diminish.
 47. A plant for the metals removalby biosorption from mining or industrial effluents in accordance withclaim 28, wherein said precipitation by pH rising pre-treatment systemcomprises at least: a neutralization reactor with a stirrer; a settlingtank; and a feed tank (also called buffer tank).
 48. A plant for themetals removal in accordance with claim 47, wherein betweenprecipitation by pH rising and biosorption said method also comprises achitosan binding stage.
 49. A plant for the metals removal in accordancewith claim 48, wherein said chitosan binding stage comprises, at least,two adsorption columns filled with chitosan.
 50. A plant for the metalsremoval in accordance with claim 28, wherein said plant for the metalsremoval can be built inside of a mobile container, of the shipping type,provided of inner walls, a ceiling and a thermically isolated floor andwith a washable covering and provided of, at least, one door and onewindow and an air conditioning system to control the inner temperaturein places with different weather conditions, which allows to transportit and evaluate the performance of said plant.